The Energy Blog has some more about cellulosic ethanol and how this alternative fuel is closer to being a sustainable fuel than gasoline. U.S. Department of Energy data indicates “that for every one unit of energy available at the fuel pump, 1.23 units of fossil energy are used to produce gasoline, 0.74 of fossil energy are used to produce corn-based ethanol, and only 0.2 units of fossil energy are used to produce cellulosic ethanol.”
I immediately began to wonder how advantageous cellulosic ethanol compares to “grass power“? Renewable Energy Access chastized Professor Pimentel and took issue with his claims that burning biomass in the production of fuel from hydrogen conversion is a better form of renewable energy than converting biomass to biofuel. They argued that Pimentel in the March 2005 paper published in Natural Resources Research based his analysis on only one conversion technology.
I remained unconvinced because their argument, actually spin to promote a product, used projections rathen than production data. In their article they admitted that ethanol production is yet to be cost-competitive while pointing to a targeted cost of $1.30 per gallon for cellulosic ethanol produced by enzymatic reduction hydrolosis. The authors asserted that in comparison to acid hydrolysis and thermal gasification this process is the most efficient means of ethanol production from cellulosic feedstocks.
People like Engineer-Poet recommend cogeneration as the best use of biomass. Burn the crop residues (leaves, stalks, and cobs) along with perennial feedstocks harvested from marginal use areas having been grown without the benefit of fertilizer, irrigation, or pesticides, e.g., fast-growing hays like switchgrass and short-rotation woody crops like poplar for combined heat and power. Then use the electricity to charge the batteries in your electric vehicles.
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While the Engineer Poet is correct in his statements about burning corn for CHP being more efficient than using it to produce ethanol, the question is where are we going to get liquid fuels to power our current generation of vehicles. According to Hirsh it takes 15 years before a new vehicle can have a significant impact on a fleet. Buying habits will change as energy gets more expensive, but they have to have a suitable product to buy. I don’t see any practical plug-in vehicle or all electric being introduced before 3-5 years. So it probably will be 20 years before they are common. With short range all electrics recharging during commuting could aggravate our power supply. Most families want at least one car with a range of 300 to 400 miles so we have to wait until battery technology is good enough for this, if it ever happens. At this point charging the batteries at home becomes difficult.
In the meantime as oil depletes we need more liquid fuels which ethanol is especially suited for. As ethanol production gets more efficient it can supply perhaps 30% of our transportation fuels. Conservation could save another 20%to 30%. The combination of these two along with some electric vehicles should be able to keep up with decreasing supplies of oil. Several ethanol plants have been built using methanol produced in a waste (manure) digester to supply heat for their distillation columns. This is a good, distributed energy source. Other people generated electricity with this methanol. As far as I recall no one is cogenerating in these facilities, but that would be a great improvement.
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[...] Since I just repeated some key points that Engineer-Poet has made against ethanol, it is interesting to note that this environmentally-sensitive weblog is lulled by the idea that ethanol can be a “sustainable fuel” and so offers some of the same misconceptions that make ethanol look so attractive at first glance. This would mean ethanol would finally make sense as a fuel, because its Energy Return On Energy Invested would be positive (since the cellulose would be waste from food, it would be close to “free” in terms of energy), it could be produced in large quantities (since it would not compete with food for land), and it would be cheap (again, because it’s waste). [...]